The most common syndrome, the behavioural variant of frontotemporal dementia (FTD), is characterised by insidious deterioration in behaviour and personality.1 In large series, a high proportion of cases have been linked to mutations in either the microtubule-associated binding protein tau gene (MAPT, causing MAPT-FTD); the progranulin gene (GRN, causing GRN-FTD); or expanded hexanucleotide repeat insertions in a non-coding promoter region of open reading frame 72 on chromosome 9 (C9ORF72, causing C9ORF72-FTD). This evidence concerns the gene MAPT and frontotemporal dementia.